Luis Amell
Temp and Humidity sensor device driver.
Fork of
DHT
by 
Components
Diff: DHT.cpp
- Revision:
- 0:9b5b3200688f
- Child:
- 1:25c96950b6ed
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/DHT.cpp Mon Jul 09 19:47:43 2012 +0000
@@ -0,0 +1,233 @@
+/*
+ * DHT Library for Digital-output Humidity and Temperature sensors
+ *
+ * Works with DHT11, DHT22
+ * SEN11301P, Grove - Temperature&Humidity Sensor (Seeed Studio)
+ * SEN51035P, Grove - Temperature&Humidity Sensor Pro (Seeed Studio)
+ * AM2302 , temperature-humidity sensor
+ * HM2303 , Digital-output humidity and temperature sensor
+ *
+ * Copyright (C) Wim De Roeve
+ * based on DHT22 sensor library by HO WING KIT
+ * Arduino DHT11 library
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documnetation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS OR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "DHT.h"
+
+#define DHT_DATA_BIT_COUNT 41
+
+DHT::DHT(PinName pin,int DHTtype) {
+ _pin = pin;
+ _DHTtype = DHTtype;
+ _firsttime=true;
+}
+
+DHT::~DHT() {
+}
+
+int DHT::readData() {
+ int i, j, retryCount,b;
+ unsigned int bitTimes[DHT_DATA_BIT_COUNT];
+
+ eError err = ERROR_NONE;
+ time_t currentTime = time(NULL);
+
+ DigitalInOut DHT_io(_pin);
+
+ for (i = 0; i < DHT_DATA_BIT_COUNT; i++) {
+ bitTimes[i] = 0;
+ }
+
+ if (!_firsttime) {
+ if (int(currentTime - _lastReadTime) < 2) {
+ err = ERROR_NO_PATIENCE;
+ return err;
+ }
+ } else {
+ _firsttime=false;
+ _lastReadTime=currentTime;
+ }
+ retryCount = 0;
+
+ do {
+ if (retryCount > 125) {
+ err = BUS_BUSY;
+ return err;
+ }
+ retryCount ++;
+ wait_us(2);
+ } while ((DHT_io==0));
+
+
+ DHT_io.output();
+ DHT_io = 0;
+ wait_ms(18);
+ DHT_io = 1;
+ wait_us(40);
+ DHT_io.input();
+
+ retryCount = 0;
+ do {
+ if (retryCount > 40) {
+ err = ERROR_NOT_PRESENT;
+ return err;
+ }
+ retryCount++;
+ wait_us(1);
+ } while ((DHT_io==1));
+
+ if (err != ERROR_NONE) {
+ return err;
+ }
+
+ wait_us(80);
+
+ for (i = 0; i < 5; i++) {
+ for (j = 0; j < 8; j++) {
+
+ retryCount = 0;
+ do {
+ if (retryCount > 75) {
+ err = ERROR_DATA_TIMEOUT;
+ return err;
+ }
+ retryCount++;
+ wait_us(1);
+ } while (DHT_io == 0);
+ wait_us(40);
+ bitTimes[i*8+j]=DHT_io;
+
+ int count = 0;
+ while (DHT_io == 1 && count < 100) {
+ wait_us(1);
+ count++;
+ }
+ }
+ }
+ DHT_io.output();
+ DHT_io = 1;
+ for (i = 0; i < 5; i++) {
+ b=0;
+ for (j=0; j<8; j++) {
+ if (bitTimes[i*8+j+1] > 0) {
+ b |= ( 1 << (7-j));
+ }
+ }
+ DHT_data[i]=b;
+ }
+
+ if (DHT_data[4] == ((DHT_data[0] + DHT_data[1] + DHT_data[2] + DHT_data[3]) & 0xFF)) {
+ _lastReadTime = currentTime;
+ _lastTemperature=CalcTemperature();
+ _lastHumidity=CalcHumidity();
+
+ } else {
+ err = ERROR_CHECKSUM;
+ }
+
+ return err;
+
+}
+
+float DHT::CalcTemperature() {
+ int v;
+
+ switch (_DHTtype) {
+ case DHT11:
+ v = DHT_data[2];
+ return float(v);
+ case DHT22:
+ v = DHT_data[2] & 0x7F;
+ v *= 256;
+ v += DHT_data[3];
+ v /= 10;
+ if (DHT_data[2] & 0x80)
+ v *= -1;
+ return float(v);
+ }
+ return 0;
+}
+
+float DHT::ReadHumidity() {
+ return _lastHumidity;
+}
+
+float DHT::ConvertCelciustoFarenheit(float celsius) {
+ return celsius * 9 / 5 + 32;
+}
+
+float DHT::ConvertCelciustoKelvin(float celsius) {
+ return celsius + 273.15;
+}
+
+// dewPoint function NOAA
+// reference: http://wahiduddin.net/calc/density_algorithms.htm
+float DHT::CalcdewPoint(float celsius, float humidity) {
+ float A0= 373.15/(273.15 + celsius);
+ float SUM = -7.90298 * (A0-1);
+ SUM += 5.02808 * log10(A0);
+ SUM += -1.3816e-7 * (pow(10, (11.344*(1-1/A0)))-1) ;
+ SUM += 8.1328e-3 * (pow(10,(-3.49149*(A0-1)))-1) ;
+ SUM += log10(1013.246);
+ float VP = pow(10, SUM-3) * humidity;
+ float T = log(VP/0.61078); // temp var
+ return (241.88 * T) / (17.558-T);
+}
+
+// delta max = 0.6544 wrt dewPoint()
+// 5x faster than dewPoint()
+// reference: http://en.wikipedia.org/wiki/Dew_point
+float DHT::CalcdewPointFast(float celsius, float humidity)
+{
+ float a = 17.271;
+ float b = 237.7;
+ float temp = (a * celsius) / (b + celsius) + log(humidity/100);
+ float Td = (b * temp) / (a - temp);
+ return Td;
+}
+
+float DHT::ReadTemperature(eScale Scale) {
+ if (Scale == FARENHEIT)
+ return ConvertCelciustoFarenheit(_lastTemperature);
+ else if (Scale == KELVIN)
+ return ConvertCelciustoKelvin(_lastTemperature);
+ else
+ return _lastTemperature;
+}
+
+float DHT::CalcHumidity() {
+ int v;
+
+ switch (_DHTtype) {
+ case DHT11:
+ v = DHT_data[0];
+ return float(v);
+ case DHT22:
+ v = DHT_data[0];
+ v *= 256;
+ v += DHT_data[1];
+ v /= 10;
+ return float(v);
+ }
+ return 0;
+}
+
+